Thread by @0xCygaar

"L2s are about as secure as centralized AWS servers".

I've seen this piece of misinformation float around quite a bit, so lets correct it.

Here's an explanation of how L2s (in their ideal form) inherit the security properties of Ethereum:

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Let's start by defining the 4 security properties of a blockchain (as defined by @sreeramkannan):

1) Re-org resistance - measures how likely it is for blocks to be re-ordered in the future

2) Censorship resistance - measures how easy it is to censor transactions

3) Data availability - can full nodes access the data required to verify the state of the chain

4) Validity - transactions must adhere to the rules of the chain (no double spending, valid state transitions, cryptographically secure)

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The question then is whether L2s inherit these security properties from Ethereum. The answer is yes.

1) L2s post data batches to Ethereum and use the L1 to determine the final ordering of txs. Once finalized on Ethereum, txs cannot be re-orged. ✅

2) A malicious sequencer can censor txs. However, most rollups include a force inclusion function that allows txs to be sent directly to the L1, bypassing the sequencer. The only way to censor these txs is to censor Ethereum itself. ✅

3) L2s post their data batches to Ethereum (I'm referring to true rollups, not validiums/optimiums). The data for re-creating the current state of the chain will always be available as long as Ethereum is live. ✅

4) The validity of a rollup's canonical bridge is determined by smart contracts on Ethereum, which accept either zk or fault proofs to advance forward. The only way to violate the rules of this bridge would be to violate the validity of Ethereum smart contracts. ✅

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The caveat to everything above is that most rollups today still have multisigs that can change the state and logic of a rollup's validating bridge. This can affect a rollup's validity property as the rules of an L2's STF can effectively be ignored. The hope for most rollups is for the multisig to be eventually removed, mitigating this risk vector.

In any case, a sequencer going down will not kill the chain as if it were a single instance AWS server. The chain's state can always be derived from data posted to Ethereum, txs can be force included via submission on L1, and funds can be withdrawn if necessary.

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A rollup sequencer is much different than an L1 blockchain with a single validator. The whole point of a rollup in the first place is to derive security from its base layer. The AWS allegations will be beat.